Hoisting apparatus



D. A. WALLACE HOISTING APPARATUS Nov. 27, 1951 4 Sheets-Sheet 1 Filed Sept. 20, 1947 INVENTOR. mm) WALLACE.

fire/WW7)? N 1951 o. A. WALLACE HOISTING APPARATUS 4 Sheets-Sheet 2 Filed Sept. 20, 1947 mmvrdn DA V/D A WALLACE BY wry/ M NOV- 27, A. WALLACE HOISTING APPARATUS Filed Sept. 20, 1947 4 sheets-sheet s IN ENT R.

V 3.2. DAVID A W/ILL. as

i7'7'0 RIVER Nov. 27, 1951 A WALLACE 2,576,908

HOISTING APPARATUS E-J-E- Patented Nov. 27, 1951 HOISTING APPARATUS David A. Wallace, Grosse Pointe Farms, Micln, assignor to Walco, lnc., Detroit, Mich., a corporation of Michigan Application September 20, 1947, Serial No. 775,191

28 Claims. 1

This invention relates to an improved hoisting apparatus and is an improvement of the hoisting apparatus shown in my patent applications Serial Nos. 653,386 flied March 9, 1946, and 711,649 filed November 22, 1946.

More specifically the invention pertains to improvements in hoisting apparatus which is particularly adapted ior hoisting vehicles.

The hoisting apparatus disclosed in my above prior applications includes a pair of hoisting units, one for application to each of the respectively opposite end portions of a vehicle and each hoisting unit comprises a fluid pressure operable extensible boom member which is adapted to be disposed in a substantially horizontal and contracted position for receiving a load. The load may thereafter be elevated by first rotating the contracted boom members to a substantially vertical position and then extending the boom member vertically to further elevate the load. Rotation of the contracted boom member occurs, in the structure of the above applications, about an axis at or adjacent one end of the boom member and accordingly considerable space is required in advance of the hoisting apparatus in order to accommodate the resulting swinging movement of the load.

It is one of the main objects of this invention to provide in hoisting apparatus of this kind, an extensible boom member and means for shifting it, which confines the initial movement of the load which occurs during translations of the boom members from their horizontal to their vertical positions, to a generally vertical path, thereby rendering it unnecessary to provide space in advance of the hoisting apparatus for accommodating swinging movement of the load.

Other objects of the invention are to provide improved toggle acting mechanism for shifting the boom members from horizontal to vertical positions which moves the load supporting ends of the boom members in a generally vertical path; to provide toggle acting mechanism of this kind which has a favorable initial mechanical advantage as it shifts the boom member from its most horizontal position and a rapidly increasing and more favorable mechanical advantage as the boom is shifted toward its vertical position, to provide energy accumulating means in hoisting apparatus of this kind which is energized during elevating the boom member through a portion of its increased mechanical advantage operating stage and which applies the accumulated energy to accelerate lowering of the boom member toward its horizontal position. and to provide energy accumulating means of this kind which does not oppose elevating of the boom member throughout the initial stages of its movement from a horizontal position when the mechanical advantage of the boom member and toggle acting means is at its lower value range.

A further object of the invention is to provide improved means for retaining a load receiving seat which is pivotally attached to each boom member in a predetermined position with respect to a horizontal plane during shifting of the boom member from its horizontal position to its vertical position and during reverse movement of the boom member.

Still further objects of the invention are to provide in a hoisting unit of this character, means for opposing unintended extension of the boom member during movement from its horizontal position to its vertical position, and to provide safeguarding'means of this kind which is ineiiective to oppose extension of the boom member when the latter is in its vertical position.

Additional objects of the invention are to provide an improved fluid pressure supply system for the boom shifting and boom extending mechanism of hoisting apparatus of this character. to provide an automatic valve mechanism which prevents the supply of fluid pressure to the boom extending mechanism prior to movement of the boom member to a predetermined upright position, to provide valve mechanism of this kind which automatically conditions the fluid pressure system to supply pressure to the boom extending apparatus immediately upon movement of the boom member to said predetermined upright position; to provide in valve mechanism of this kind means for assuring contraction of the boom member before it is shifted to its horizontal position. to provide valve mechanism of this kind which automatically conditions the fluid pressure system to release the fluid pressure retaining the boom member in a vertical position immediately upon contraction of the boom member from an extended position, to provide a fluid pressure system of this kind which assures contraction of the boom member before it shifts to a horizontal position in the event of a leak or break in the fluid pressure line which leads from a source of fluid pressure to the automatic valve mechanism and to provide automatic valve mechanism of this kind which will assure contraction of the boom member from an extended position at a faster rate than the boom member is shifted toward its horizontal position in the event of a relatively slow leak from the cylinders of the boom shifting mechanism or in any of the pressure lines leading thereto.

An illustrative embodiment of the invention is shown in the accompanying drawings in which:

Figure 1 is a side elvational view, partly in section showing hoisting apparatus embodying the invention as applied to the hoisting of a vehicle.

Figure 2 is a fragmentary plan view of the hoisting apparatus shown in Figure 1. illustrating one hoisting unit thereof, somewhat in detail.

Figure 3 is a longitudinal vertical sectional view taken on line 3-3 of Figure 2.

Figure 4 is a fragmentary vertical sectional view taken on the line H of Figure 2.

Figure 5 is a transverse vertical sectional view taken on the line 5-5 of Figure 2. a

Figure 6 is a fragmentary transverse vertical sectional view taken on the line e-s of Figure 2.

Figure '1 is a transverse vertical sectional view taken on the line 1-1 of Figure 2.

Figure 8 is a fragmentary vertical sectional view taken on the line 8-! of Figure 2.

- Figure 9 is a vertical sectional view taken on the line 9-! of Figure 2.

Figure 10 is a transverse vertical sectional view taken on the line ill-iii of Figure 2.

Figure 11 is a fragmentary transverse vertical sectional view taken on the line ll of Figure 2.

Figure 12 is a fragmentary transverse vertical sectional view taken on the line it-Jl of Figure 2.

Figure 13 is a sectional view taken on the line il-II of Figure 8.

Figure 14 is a vertical sectional view of manual control valve mechanism indicated at ll in Figure 2.

The improved hoisting apparatus shown in the drawings may be mounted on the floor of a building but it is preferably disposed in a recess It provided in a floor structure It or in a relatively thin platform mounted upon a floor structure. Disposed along the longitudinal sides of the recess I! are spaced rails, generally designated by the numeral ll, each of which comprises a track member I! of channel shaped cross-section having opposite horizontal flanges is facing inwardly of the recess. The internal surfaces of the flanges is of each track member is converge outwardly from the recess. Each rail I! also includes a channel member having its web portion fixed to the web of the adjacent track member l8 and having flanges Ii extending outwardly with respect to the recess.

The hoisting apparatus shown in Figure 1 includes a pair of substantially identical hoisting units A and B, the description of one of which will serve for both. While two hoisting units are preferably employed in hoisting a vehicle, only one may be employed for lifting the ends of a vehicle one at a time. Any desired number of hoisting units may be used as required by the nature of the obiect or load to be hoisted.

Each hoisting unit includes a pair of carriages generally designated by the numerals 2! and 2! in Figure 2. The front carriage :2, as viewed in Figure 2, comprises an intermediate frame member is having shafts or trunnions extending outwardly from its opposite extremities. Journalled on each outer end portion of each trunnion 25 is a wheel It having a beveled periphery 21 which is received between the converging sides of the flanges I! of the rail members II. The rear carriage 23 comprises a yoke shaped body 4 portion I! having arms 2! at its opposite ends provided with passages Iii in which are mounted shafts 3|. The shafts II have opposite end portions projecting beyond the inner and outer extremities of the arms 20 of the yoke shaped body portion II. Journalled on the outer end portions of each of the shafts fl is a wheel 12 similar to the wheels is of the front carriage 22. The wheels I! fit between the flanges is of the rail members is in the same manner as do the wheels 2|.

Pivotally mounted on the inwardly extending end portion of the shafts II is a boom member generally designated by the numeral 33. The boom member II includes a pair of piston and cylinder assemblies each having a cylinder 34 and a piston 35. shown in section in Figure 9. Each piston member 35 includes a tubular piston rod portion ll of substantially smaller outer diameter than the inner diameter of the cylinder 34. Each piston portion has a boss element 31 which is received in the passage of its tubular connecting rod 36 and secured thereto by a pin 30 extending through registering apertures in the tubular piston rod 3' and boss 31. Each piston ll has a cap member 38 on the end thereof opposite from the boss I! which bears against a packing ring 40 provided in a recess 4| formed in the body portion of the piston. The cap 39 may be clampingly engaged with the packing ring to by a bolt 42 extending through the cap and which is threaded in the body portion of the piston 38. The right hand end of each cylinder 34, as viewed in Figures 2 and 9, is closed by a cap structure ll having a projecting web portion ll provided with an aperture 4! in which one of the inwardly extending end portions of each shaft 3|, respectively, is received. In this manner, the right ends of the cylinder and piston assemblies of the boom structure are pivoted to the rear carriage It for rotative movement about the axes of the shafts 3i which are aligned.

The cylinders 34 of the boom member are rigidly connected together and held in spaced relationship by transversely extending cleat members ll and l! which are located at the right and left end portions of the boom member, respectively, as shown in Figure 2. The cleats it and 41 are substantially identical and one thereof is shown in section in Figure 12. The boom member 33 is also transversely rlgidiiled at its intermediate portion by a cleat member 48 shown in section in Figure 5. The cleat members It, 41, and ll have apertures which receive the cylinder members I and the cleat member 48 is additionally provided with trunnicns 49 which extend outwardly in opposite directions from the end portions of the cleat 4t. Journalled on each outwardly extending end portion of each trunnion I9 is a bearing 50 provided at one end of a link II, respectively. Each link 5| has a bearing 82 at its opposite end which is journalled on an intermediate portion of one of the trunnions II of the front carriage 22, respectively, at a location between the frame member 24 of the carriage and a wheel 2! thereof. The cleats 46, I1 and .8 are all welded or otherwise rigidly secured to the cylinders ll of the boom member.

The outer ends of the connecting rod portions 38 of the piston members are connected together by a transversely extending bar 53 shown in section in Figure 11, which is of generally crescent shape. This bar has recesses 54 in its opposite end portions in which the outer extremities of the piston rod portion II are received. The outer ends of the piston rod portions may be welded or otherwise suitably secured to the bar II. Extending rightwardly as viewed in Figure 2, from the bar]! are lugs It on which a load receiving seat, generally designated by the numeral BI, is pivoted. The load receiving seat is adapted to engage and support one end of a vehicle or other object to be lifted and it comprises a body portion [1 having two pairs of spaced flanges I! each of which is adapted to embrace one of the lugs II of the bar 53. The lugs 55 and flanges II are provided with registering apertures in which pins 58 are received for providing a pivotal connection between the seat 58 and the bar II. The seat 68, shown in Figure 10, is particularly designed to receive a rear axle portion of the vehicle. It is provided with pivotally mounted crotch members Bil having notches Si in their upper extremities. These crotch members may be rotated between vertical operative and horizontal inoperative positions about their respective pivots 62. It should be understood that the load receiving seat portion of each of the hoisting units A and B are designed to receive the particular portion of the vehicle or other load to which they are intended to be applied.

It will be seen in Figures 3 and 8 that the flanges 68 of the load receiving seat 56 are provided at the right edge of the structure 56 and that they depend downwardly from its body portion 51. Provided substantially midway between the ends of the body portion 51 of the seat 58 is a downwardly and leftwardly extending flange '3 to which is pivoted one end of a telescoping control rod, generally designated by the numeral ll. The control rod 84 comprises a lower tubular section 65 which is pivotally mounted at its lower end, or right end as viewed in Figure 2, to an extension 66 of the yoke shaped bod portion 28 of the right hand carriage 23. This pivotal connection is formed by a pin II which extends through registering apertures. In the extension II and in spaced flanges 68 extending rightwardly from the right end of the tube 65 the telescoping control rod 64 includes an inner bar member 69 which is of substantially smaller diameter than the inner diameter of the tube 65 and it is provided on its left extremity, as viewed in Figure 2, with spaced flanges Ill which embrace the flange 63 of the seat structure 56. The flanges 83 and 10 are provided with registering apertures in which are received a pin II for forming the pivotal connection between the bar 89 of the telescoping control rod 64 and the seat structure 5|.

As the boom member is shifted, as hereinafter more fully described, from its lower generally horizontal position to its upper generally vertical position the control rod it maintains the load receiving seat in a substantially horizontal position throughout the entire path of movement of the boom member. This is accomplished by locating the pivotal axis of the pin 81 the same distance from the pivotal axis of the boom member in its movement about the aligned axis of the shafts Ii as the pivotal axis of the seat it and the control rod 64. This construction provides a parallelogram action which retains the seat 56 horizontal between movement of the boom member, hereinafter described. When the boom member is in its upper position, as shown in dotted lines in Figure 3, the body portion 51 is received on the side surface 12 of the cross bar II which connects the piston rod portion 38, as previously described.

when the structure so far described is employed in lifting a vehicle, for example, the forward carriage II of one of the hoisting units is flxed in position in a manner hereinafter disclosed. It is unnecessary to fix either of the carriages of the other hoisting unit in this manner for the rigid connection provided by the vehicle between the two hoisting units serves this purpose. When the vehicle or other load to be hoisted is properly positioned with respect to the load receiving seats of the respective hoisting units, the boom member 33 is shifted from its lower position in which the piston and cylinder assemblies thereof are in contracted state, to its upper position, shown in dotted lines in Figure 3. by urging the rear carriage 2! of each unit toward the forward carriage II of each unit respectively. This action is performed by fluid pressure mechanism, hereinafter more fully described. During movement of the rear carriage 23 toward the front carriage 22 the rear carriage is held against upward movement by engagement of its wheels 32 with the flanges iii of the rails II. The end of the boom member by which the seat It is supported is urged upwardly by a somewhat toggle-like action provided by the links II which shifts the lower end of the boom member horizontally in a direction opposite to the horizontal component of the pivotal movement of the boom member about its pivotal axis provided by the shafts 3|. This causes the load receiving seat 58 to ascend in a path which departs but slightly from a vertical course. While the path of movement of the seat It is not truly vertical it is much more so than would be obtained by merely rotating the boom member about a flxed axis and as a result less space is required in advance of the hoisting structure to accommodate upward shifting of the boom member.

' There is also a mechanical advantage gained in this hoisting action. The mechanical advantage of the system is at a lower value during initial shifting of the boom member from its lower position than during subsequent shifting of the boom member toward its upright position. The same action takes place during lowering of the boom member from its upper to its lower position. As will be hereinafter set forth in greater detail, the boom member may be extended after it is in its upright position to further elevate the load.

The upper end of the tubular part of the extensible guide bar M is provided with oppositely extending trunnions It on which are pivotally mounted links-ll, as shownin Figures 2 and 8. The other ends of the links ll, are secured by pins 15 to spaced pairs of flanges ll extending leftwardly as viewed in Figure 2 from the cleat 48. The links 14 serve to hold the boom structure against unintended extension when the boom member is displaced from its substantially upright position. It will be seen in Figure 8 that the eflective lengths of the links 14 are equal to the distance between the pivotal axis of the seat ll established by the pins 58 and the pivotal connection of the flange 61 on the seat with the extensible rod 58 of the control bar. Any tendency of the piston and piston rod portions of the boom structure to extend outwardly while the boom member is in its horizontal and initially elevated positions tends also to disturb the parellelogram geometry which the links 14 form with the span between the pivots i9 and 1 I. Thus the outward urge of the piston and piston rod portion of the boom member tends to rotate th seat 88 in a counterclockwise direction, as viewed in Figure 8, about the pivot 88. Such turning of the seat 88 about the pivot 88 is opposed by the links I8 and guide bar which cannot be readily moved from its relation with respect to the longitudinal axis of the boom member while the boom member is substantially displaced from its ver-- tical position.

It will be seen in Figures 1 and 3 that when the boom member is in its upright position it is slightly displaced to the left of a true vertical plane. This arrangement is provided to assure downward rotation of the boom member in a counterclockwise direction, as viewed in these figures. It will also be noted that the guide member 88 is not exactly parallel to the boom member in Figures 1 and 3. Such displacement from a truly parallel relationship is accommodated by the space shown in Figure 8 between the inner and outer telescoping parts 88 and 65, respectively, of the guide bar 88 which provides free action of the parts of the mechanism.

Each hoisting unit is provided with fluid pressure actuating mechanism by which the boom member is shifted bodily from its horizontal to its vertical position and which also extends the boom member axially to further elevate a load supported on the seat 88. The actuating mechanism which bodily shifts the boom members comprises a pair of cylinders II which, as shown in Figures 2 and 1 are shiftably carried by a carriage generally designated at 18. The carriage I8 has a main body portion 18 provided with trunnions 88 on which wheels M are journalled. The wheels 8| are received between the flanges l8 of the track member 18 in the same maner as the wheels 21 and 82 are engaged with the track member iii. The body portion 18 of the carriage 18 is provided with spaced openings 88 in which the cylinders 11 are received and these cylinders may be welded or otherwise suitably secured to the body member I8 of this carriage.

As shown in Figure 9 the left end of each cylinder I1 is provided with a cap member 88 in which is provided a gland generally designated by the numeral ll in which a piston rod 85 is slidably received. Each piston rod 85 has a piston 88 on its right end disposed in one of the cylinders l1, respectively. Formed on the left extremity of each cap 88 is a collar 81 which surrounds the gland 88 and which is received in a circular opening 88 of the body portion 28 of the carriage 28. The collars 81 and cylinders to which they are attached are fixed to the body portion 28 of the carriage 28 by set screws, one of which is shown at 88 in Figure 9. The caps 88 are each provided with a fluid pressure passage 88 which communicates at one end with the interior of one of the cylinders 11. The other end of each passage is connected to one end of a U-shaped conduit III of a fluid pressure supply system hereinafter more fully described.

The piston rods 88 extend leitwardly from the carriage 28 thru registering apertures in the body portion 28 of the front carriage 22 and in a channel bar 88 which extends transversely between the ends of the parallel track members H to which they are attached by bolts 88. The left end portions of the piston rods are threaded and provided with nuts 84, one located on each opposite side of the web of the channel bar 82, as shown in Figure 8. The nuts 88 clampingly hold the carriage 22 in fixed position adjacent the channel bar 82 and also flx the left ends of the piston rods 88 against movement. When fluid pressure is admitted to left ends of the cylinders II, the cylinders and the carriage 28 together with the right end of the boom member are forced leftwardly as viewed in Figure 2, the pistons and piston rods remaining stationary. This action, as previously described, shuts the boom member from its horizontal to its vertical position under the control of the links 8| which confine the movement of the lelt end of the boom member and seat 58 thereon to a path which does not depart greatly from a vertical course.

A helical spring 88 surrounds each of the piston rods and extends from the rear carriage 28, leftwardly as viewed in Figure 2, to a location spaced substantially from the front carriage II. l'ls the cylinders 11 initially move toward the front carriage 82 the springs are also shifted in the same direction until their left extremities engage the body portion of the carriage 22. During the initial shifting of the carriage which corresponds to this initial shifting of the cylinders, the load is elevated under a relatively unfavorable mechanical advantage. During further upward movement of the boom member, the mechanical advantage improves and it is during this stage of the operation that the springs 88 are compressed and loaded for the purpose of assisting in the initial stages of the boom lowering operation.

While the mechanical advantage of the system is lower when the boom member is in its lowermost position than in any of its other positions, it is improved considerably at the lowermost position of the boom member because of the location of axis of each trunnion 88, as shown in Fig. 3. The location of the axes of the trunnions 88 of each unit above the plane deflned by the pivotal axis of the lower ends of the links SI and the pivotal axis of the boom member thereof as when the boom member is in its lower position as shown in Fig. 8, prevents unintended locking of the boom member 88 and links Si in an aligned relationship and also provides a greater mechanical advantage during initial lifting of the load. Since the minimum mechanical advantage in the leverage system embodied in the above described hoisting apparatus occurs when the boom members are in their lowermost positions, increasing of the mechanical advantage at this end of the range of movement significantly reduces the maximum power requirements and size of the driving mechanism.

The fluid pressure system by which the boom is both shifted and extended comprises an automatic valve mechanism. generally designated by the numeral 86 in Figure 2. This valve mechanism shown in detail in Figure 13, has an inlet port 81 which is connected by a conduit 88 with the U-shaped conduit 8| so as to simultaneously supply fluid medium to both cylinders 11. The automatic valve 88 has another port 88 which is connected by a conduit I88 with a U-shaped conduit I8l havin opposite end portions communieating with the interior of the cylinders 3|, respectively, of the boom member at a location on the right side of the pistons 85 which are disapropos ignated by the numeral WI. The compressor I01 has an inlet which is connected by a conduit I03 with a source or tank I03. The manual control valve I3 also has an outlet port I I which is connected by a conduit I I I with the inlet of the tank I03. A branch conduit II2 including a section of hose II3 connects the conduit III with the automatic valve. for draining fluid medium from the latter in conveying it to the tank I00 for the purpose hereinafter set forth.

The manual control valve II has a bore II3 with which the ports I03; IIO and I05 communicate. Shiftably mounted in the bore H3 is a valve element II3 having spaced piston like portions II3, Ill and H3 which are so disposed as to establish communication between the inlet port I03 and the outlet port IIO when the valve element H3 is disposed in the position shown in Figure 14. The piston portions II3, Ill and H3 sealingly engage the wall of the bore H3 and when the valve element H5 is in the position shown the piston portion IIl blocks the flow of fluid medium from the inlet port I03 to the outlet port I03. This setting of the valve element II3 by-passes fluid pressure from the inlet port I03 thru the outlet port H0 and conduit III and the piston portion Ill blocks the reverse flow of fluid pressure from the automatic valve mechanism and port I03. The valve element II3 may be shifted in opposite directions from the position shown in Figure 14 by a handle II3 pivotaliy attached at I23 to the valve element H3. The lower end of the handle I I3 is swingably supported by a link I which is pivotally attached at one end at I22 to the casing of the manual control valve I3 and at its other end to the handle H3 at I23.

When the valve element H3 is shifted leftwardly from the position shown in Figure 14 sufflcleniiy to bring the piston port III to the left side of the outlet port I03, communication is established between the inlet port I03 and both outlet ports I03 and Ill and thus fluid pressure is exhausted from the conduit I03 and inlet port I02 of the automatic valve 33 and at the same time the fluid pressure supplied by the compressor I01 is by-passed thru the port IIO to the tank I03. The outlet port III! is of ample capacity to relieve the pressure from the automatic valve 36 and at the same time accommodate the return to the tank of fluid medium supplied by the compressor.

The automatic valve mechanism 33 includes a valve casing I23 in which are formed upper and lower parallel bores I25 and I23. The upper bore I25 communicates with the outlet ports 31 and 33 and the lower bore I23 communicates with the inlet port I 02. Provided in a partition element I21 which separates the bores I23 and I23 is a large passage I28 and a smaller passage I23 both of which connect the bores I25 and I23. A valve member I23 is shiitably mounted in the upper bore I25 and provided with piston-like valve elements I30 and I3I which closely lit the wall of the bore. The right end of the upper bore I25 is closed by a threaded plug I32 against which the valve member I23 is yieldably held by a spring I33 which bears between the piston-like valve element I30 and a hollow cap I33 which is threaded in the left end of the bore I23.

A valve member I35 is shiftably mounted in the lower bore I23 and provided with piston-like valve elements I33 and I31 which closely at the wall of the bore. The valve member I33 is yieldably urged leitwardly, as viewed in Figure 13. by

a spring I33 which bears between the valve element I31 and a shoulder I33 formed within a nipple I30 which is threaded in the right end of the bore I23. The conduit H2 is threaded in the outer end of the nipple I33.

Provided on the left end of the valve member I33 is a stem I which is slidably received in sealing engagement in the passage of a gland element I32 threaded in the left end of the bore I23. The stem I3I of the valve member I33 is connected by a coupling I33 with a rod I33 which is axially shiftabiy mounted on the carriage 23. as shown in Figure 2. The automatic valve 33 is supported on a bracket I33. also shown in Figure 2. which is carried by one of the cylinders TI. The rod I33 and automatic valve mechanism 33 with which it is associated shifts in unison with the carriage 23 and the left end of the rod I33 is adapted to engage an abutment I33 mounted on the front carriage 22 when the rear carriage 23 has been shifted leftwardiy. as viewed in Figure 2, sufllciently to bring the boom member to its upright position. Engagement of the rod I33 with the abutment I33 during the final stage of upward shifting movement of the boom member urges the valve member I33 rightwardly against the action of the spring I33.

Operation of the valve mechanism. shown in Figure 14. takes place in the following manner. The manual control valve handle H3 is turned in a clockwise direction to supply fluid medium to the outlet port I03 which passes thru the conduit I03 to the inlet I02 of the automatic valve. With the valve member I23 and I33 in the position shown in Figure 13. the fluid pressure medium flows directly thru the passage I23, bore I23, outlet port 31. conduit 33 and U-shaped conduit 3i to each of the cylinders 11. The fluid medium continues to flow into the cylinders 11 until the boom member has been shifted from its horizontal to its vertical position. As the boom member approaches its vertical position the valve element I35 is shifted rightwardly against the spring I33 by engagement of the rod I33 with the abutment I33. This action brings the piston-like valve element I31 to the right side of the small passage I23. The pressure of the fluid medium admitted thru the passage I23 to the bore I23 shifts the valve member I23 leftwardly. as viewed in Figure 13. against the action of the spring I33 until the valve-element I3I is entirely disposed on the left side of the passage I23. The fluid pressure previously applied to the cylinders 11 is maintained therein by the obstruction of the valve element III to the reverse flow of fluid medium from the outlet 31. When the valve member I33 is in its left position fluid medium flows from the inlet I02 thru the bore I23. passages I23 and I23. bore I23. outlet 33. conduit I00 and U-shaped conduit IOI into the cylinders 33 of the boom member thereby extending the boom member while it is in its upright position. The valve mechanism thus automatically supplies fluid medium to the cylinders 33 until the boom member is in this condition.

When it is desired to lower a vehicle or other load supported on the upright extended boom members of the pair of hoists, shown in Figure 1. the manual control valve handles are shifted in a counterclockwise direction to move the valve member II3 leftwardiy, as viewed in Figure 14, until communication is established between the ports I03, III and I33. This exhauts fluid pressure from the bore I 23 of the automatic valve 33. The upper valve member I23, however. is

held in its left-hand position by the fluid pres sure on the right side of the valve element I8I while fluid pressure is exhausted from the cylinders 84 thru the U-shaped conduit I8I, conduit IIIII, port 88, bore I28, passages I28 and I88, bore I28, port Hi2 and conduit I03. This exhausting of fluid medium from the cylinders 84 accommodates contraction of the boom member which remains in its upright position until the piston and piston rod portions of the boom member are fully contracted. Pressure on the right side of the valve element III is reduced sufliciently to al ow the spring I88 to shift the valve member I28 rightwardly to the position shown in Figure 13. Fluid pressure then flows from the cylinders 11 thru the port 81, bore I28, passa e I28, bore I26, outlet Ill! and conduit I88 to the tank I08, thereby permitting the boom member to be shifted downwardly, initially by the combined action of the load and springs 85 and subsequently only by the load. until the boom member reaches its horizontal position. As the boom member departs from its u right position, the rod I parts contact with the abutment I48 and the spring I88 returns the valve member I88 to the position shown in Figure 15. Thus the automatic valve mechanism 88 automatically causes shifting of the boom member from its upright to its horiaontal position after the boom member has been fully contracted and prevents such shifting of the boom member until it is fully contracted.

When the boom member is extended and in its upright position the valve element I3I blocks the return flow of fluid medium from the cylinders ll. Any small leak which might occur in the portion of the fluid system which supplies fluid medium from the source to the automatic valve would merely cause the boom member to be lowered in its usual way. Contraction of the boom member would take place before it shifted from its vertical to its horizontal position for the valve element I8! would remain in obstructing relation to back flow of fluid medium from the cylinders 11 until all pressure had been relieved on the right side of the valve element III.

A slow leak at the cylinders II or in the conduits leading from the automatic valve 88 would result in a slight downward shifting of the boom member while in its extended condition. However this slight movement would disengage the end of the rod I from the abutment H6 and allow the spring I88 to shift the lower valve member I85 leftwardly, as viewed in Figure 15 and permit free flow of fluid medium from the cylinders 84 of the boom member, the fluid medium would then be returned from the right end of the bore I28 thru the passage of the nipple III! and thru the conduit III to the tank I08. This free flow of fluid medium from the cylinders 8| would result in contraction of the boom member at a much faster rate than it was permitted to shift toward its horizontal position and accordingly, the boom member would be fully contracted long before it rotated in an extended condition to a dangerous position.

In the foregoing disclosure of the structure and operation of the improved hoisting apparatus it will be seen that provision is made for shifting the load upwardly in a path which does not depart far from the vertical course, thus eliminating the necessity of providing adequate room to accommodate swinging oi the load about an axis. The apparatus is also provided with springs for urging the boom downwardly from its vertical movement when such movement tends to occur at a slow rate. These springs are energized during the stage of upward movement when a favorable mechanical advantage is present and therefore provision of additional power over that required during the initial shifting of the boom member from its horizontal position is not required. Dependable self acting safeguard mechanism is provided for preventing unintended extension of the boom member prior to movement thereof to its upright position. A fluid pressure system is provided for operating the hoist and has a fully automatic valve mechanism which assures contraction of the boom before it is rotated downwardly under all conditions. This valve mechanism also automatically causes the contraction and shifting and the extension and shifting of the boom member to automatically occur in proper sequence.

Although but one specific embodiment of the invention has been herein shown and described it will be understood that various changes in the details and construction thereof may be made without departing from the spirit and scope of my invention.

I claim:

1. Hoisting apparatus comprising a boom member, a load receiving seat on one end portion of said boom member, means shiftably and pivotally supporting the opposite end of said boom member, means for holding said first mentioned means against displacement from a horizontal plane, a link member terminating at and pivotally connected at one end only with said boom member at a location between said seat member and supporting means, a fixed pivot member pivotally supporting the other end of said link member, and mechanism for shifting said opposite end of said boom member to move it from a generally horizontal to a generally vertical position.

2. Hoisting apparatus comprising a boom member shiftable between generally horizontal and vertical positions. a load receiving seat on one end portion of said boom member. a support linearly shiftably and pivotally supporting the opposite end of said boom member. a link member pivotally attached to said boom member at a location between said seat member and support and extending away from said opposite end of said boom member when the latter is in its generally horizontal position, a flxed pivot member pivotally supporting the other end of said link member, and mechanism for shifting said boom member from its horizontal to its vertical position including an actuating element for urging said opposite end of said boom member toward said fixed pivot, said actuating element including power actuated means mounted on said support and extending away from said fixed pivot member so as to accommodate movement of said opposite end of said boom member into close proximity to said flxed pivot member.

8. Hoisting apparatus comprising a boom member shiftable between horizontal and vertical positions. a load receiving seat on one end portion of said boom member, a support linearly shiftably and pivotally supporting the opposite end of said boom member. a base structure shiftably receiving and cooperating with said support and including means for holding said support and said opposite end of said boom member against movement in opposite directions transverse with respect to the path of linear shifting movement of said support. a link member pivotally attached at position during initial stage of its downwa d 76 one end to said boom member at a location intermediate its end portions, a pivot fixed with respect to said base structure and pivotally supporting the other end oi said link member. said pivot being spaced from said first mentioned end of said link member in a direction opposite from said support, and actuating mechanism for shiiting said support toward said fixed pivot to elevate said boom member.

4. Hoisting apparatus comprising a boom member including first and second relatively axially extensible and contractable sections and means for axially shiitably guiding and supporting said first section on said second section, a load receiving seat on one end of said first section, means shiftably and pivotally supporting the opposite end of said second section, a link member pivotally connected at one end with said second section of said boom member at a location spaced from said supporting means, a pivot member pivotally supporting the other end oi said link member, mechanism for shifting said opposite end of said last mentioned boom section to move said boom member from a generally horizontal to a generally vertical position, and mechanism for relatively axially extending said boom member sections. 7 5. Hoisting apparatus comprising a boom member including first and second relatively axially extensible and contractable sections and comprising means for axially shiftably guiding and supporting said first section on said second section, a load receiving seat on one end of said first section, a support linearly shiitably and pivotally supporting the opposite end oi said second section of said boom member, a base structure shii'tably receiving and cooperating with said support for holding it against movement in a direction transverse to its path oi. linear shifting movement, a link member attached at one end to said second boom section at a location intermediate its end portions,a pivot carried by said base structure and pivotally supporting the other end of said link member, said pivot being spaced from said first mentioned end of said link member in a direction opposite from said support, actuating mechanism for shifting said support toward said fixed pivot to elevate said boom member, and actuating means for relatively axially extending said boom sections.

6. Hoisting apparatus comprising a boom member, a load receiving seat on one end portion of said boom member, means shiitably supporting said boom member for combined pivotal and translative movements between generally vertical and generally horizontal positions, actuating mechanism for shifting said boom member from said generally horizontal position to said generally vertical position, and energy accumulating mechanism energizable only by the shifting of said boom member from a position intermediate its generally horizontal and generally vertical positions to its generally vertical position for urging said boom member toward its generally horizontal position.

7. Hoisting apparatus comprising a boom member, mechanism for shiitably supporting and positively drivingly shifting said boom member from an approximately horizontal to an approximately vertical position, said mechanism comprising a system of levers having a lower mechanical advantage during initial portions of its stage boom shifting movement from a horizontal position than during subsequent portions of such stage oi movement and including power actuating mechanism, and energy accumulating l4 apparatus energizable by said mechanism only during said subsequent portion 6! its boom shitting movement for urging said boom member toward its generally vertical position.

8. Hoisting apparatus comprising a base structure, a boom member shii'table between generally horizontal and vertical positions, a load recciving seat on one end portion oi said boom member, means shiitably supporting said boom member on said base structure [or combined pivotal and longitudinally translative movements relative to said base structure, coacting elements on said base structure and supporting means for holding said supporting means against vertical displacement from said base structure said means including a link member tree from said load receiving seat and coacting only between said boom member and said base structure for shifting said end of said boom member and said load receiving seat horizontally in a direction opposite to the horizontal movement thereof resulting irom pivotal movement 0! said boom member to conline the movement oi said load receiving seat to an approximately vertical path.

9. Hoisting apparatus comprising a base structure, a boom member shiitable between generally horizontal and vertical positions, a load receiving seat on one end portion of said boom and means shiitably supporting said boom member on said base structure for combined pivotal and translative longitudinal movements relative to said base structure, coacting elements on said base structure and said supporting means for holding said supporting means against vertical displacement from said base structure, said means including a link member free from said load receiving seat coacting between only said boom member and said base structure for shifting said end of said boom member and said load receiving seat horizontally in a direction opposite to the horizontal movement thereoi resulting irom pivotal movement oi said boom member to confine the movement 01' said load receiving seat to an approximately vertical path, and power actuating mechanism for shifting said boom member in a path defined by said supporting means from said generally horizontal to said generally vertical position, said power actuating mechanism including driving means spaced from between said boom member and said link member.

10. Hoisting apparatus comprising a base structure, a boom member shii'table between generally horizontal and vertical positions, a load receiving seat on one end portion of said boom member and means shiitably supporting said boom member on said base structure for combined pivotal and translative movements relative to said base structure, said means includin a link member coacting between said boom member and said base structure IOr shifting said end oi said boom member and said load receiving seat horizontally in a direction opposite to the horizontal movement thereof resulting irom pivotal movement of said boom member to conline the movement oi said load receiving seat to an approximately vertical path. power actuating mechanism for shitting said boom membe in a path defined by said supporting means from said generally horizontal to said generally vertlcal position and energy accumulating apparatus energizable by shifting of said boom member toward its generally vertical position for urging said boom member toward its generally horizontal position.

11. Hoisting apparatus comprising a base memher, a boom member comprising spaced piston and cylinder assemblies, means including a shirtable pivot support shiftably mounting said boom member on said base member for combined pivotal and translative movements relative to said base member between substantially horizontal and vertical positions, an article supporting member carried by said piston members and located at one end of said boom member, said means including a link coacting between said boom and base member for shitting said end of said boom member horizontally in a direction opposite to the horizontal component of the pivotal movement of said boom during raising and lowering operations of said boom member to retain the path of movement of said end of said boom member approximately vertical, mechanism for shifting said boom member from its horizontal to its vertical position to initially liit an article on said article support to one elevation. and means including conduits for supplying fluid pressure to said cylinders for extending said pistons to lift said article to a higher elevation.

12. Hoisting apparatus comprising a base structure, a boom member comprising a piston and cylinder member shiftable between generally horizontal and generally vertical positions, a load receiving seat on said piston member located at one end of said boom member, means for shiftably supporting said cylinde member on said base structure for combined pivotal and translative movements relative to said base structure. said means including a link member coacting between said boom member and base structure for shifting said load receiving seat horizontally during pivotal movement of said boom member in a direction opposite to the horizontal movement thereof resulting from pivotal movement of said boom member to confine the movement of said load receiving seat to an approximately vertical path, fluid pressure mechanism for shifting said boom member from its horizontal to its vertical position, and fluid pressure supply apparatus for extending said piston relative to said cylinder after said boom member is in its vertical position.

13. Hoisting apparatus comprising a base structure, a boom member comprising a. piston and cylinder member shiftable between generally horizontal and generally vertical positions, a load receiving seat on said piston member located at one end of said boom member, means for shiftably supporting said cylinder member on said base structure for combined pivotal and translative movements relative to said base structure, said means including a link member coacting between said boom member and base structure for shifting said load receiving seat horizontally during pivotal movement of said boom member in a direction opposite to the horizontal movement thereof resulting from pivotal movement of said boom member to confine the movement of said load receiving seat to an approximately vertical path, fluid pressure mechanism for shitting said boom member from its horizontal to its vertical position. fluid pressure supply apparatus for extending said piston relative to said cylinder after said boom member i in its vertical position, and a spring energizable by upward shifting movement of said boom member for assisting in returning it from its vertical to its horizontal position.

14. Apparatus for hoisting a vehicle comprising a base structure, a pair of hoisting units on said base structure, each of said hoisting units including a boom member comprising a main section and a relatively extensible section, a seat on the extensible section of each of said boom members for receiving an end portion of a vehicle respectively, means shiftably supporting the main section of each of said boom members including a pair of carriages mounted on said base structure, said means including members pivotally connecting an end of each main section of each boom member with one of said carriages and a link swingably connecting an intermediate portion or each of said main sections with one oi said carriages, mechanism for shifting'the carriage supported end of each of said main sections toward the other carriage of each unit respectively for moving said boom members from generally horizontal to generally vertical positions to initially elevate said vehicle approximately vertically, and apparatus for shifting said extensible sections oi said boom member axially relative to the main sections thereof to further elevate said boom members.

15. Apparatus for hoisting a vehicle comprising a base structure, a pair of hoisting units on said base structure, each of said hoisting units including a boom member comprising a main section and a relatively extensible section, a seat on the extensible section of each of said boom members for receiving an end portion of a vehicle respectively, means shiftably supporting the main section of each of said boom members including a pair of carriages mounted on said base structure, said means including members pivotally connecting an end of each main section of each boom member with one of said carriages and a link swingably connecting an intermediate portion of each of said main sections with one of said carriages, mechanism including a fluid pressure actuated device for shifting the carriage support end of each of said main sections toward the other carriage of each unit respectively for moving said boom members from generally horizontal to generally vertical positions to initially elevate said vehicle approximately vertically, said main and extensible sections of said boom members comprising telescoping cylinder and piston elements respectively, and fluid pressure supply apparatus for feeding fluid pressure to each of said cylinder elements to shift said extensible sections axially of said main sections in order to further elevate said boom member.

16. Apparatus for hoisting a vehicle comprising a base structure, a pair of hoisting units on said base structure. each of said hoisting units including a boom member comprising a main section and a relatively extensible section, a seat on the extensible section of each of said boom members for receiving an end portion of a vehicle respectively, means shiftably supporting the main section of each of said boom members including a pair of carriages mounted on said base structure, said means including members pivotally connecting an end of each main section or each boom member with one of said carriages and a link swingably connecting an intermediate portion of each of said main sections with one of said carriages, mechanism for shifting the carriage supported end of each of said main sections toward the other carriage of each unit respectively for moving said boom members from generally horizontal to generally vertical positions to initially elevate said vehicle approximately vertically, said base structure including flanges for holding said carriages against vertical displacement, and means fixing the link supporting carriage of one hoisting unit against horizontal shitting movement relative to said base structure.

l'i. Hoisting apparatus comprising a shiitable carriage, a boom member shittable between generally horizontal and generally vertical positions and comprising a main section pivotally mounted on said carriage and a relatively axially extensible section carried by said main section, a load receiving seat pivotally mounted on said extensible section and mechanism for holding said seat in a predetermined position with respect to a horizontal plane including a guide member extending along said main boom section having one end pivotally mounted on said carriage in spaced relation to the pivotal axis 01' said main boom section and including a link swingably connecting the opposite end of said guide member to said main boom section, said mechanism including a rod member axially slidably engaged with said guide member and pivotally attached to said seat at a location spaced from its pivotal axis.

18. Hoisting apparatus comprising a shiftable carriage, a boom member shlftable between generally horizontal and generally vertical positions and comprising a main section pivotally mounted on said carriage and a relatively axially extensible section carried by said main section, a load receiving seat pivotally mounted on said extensible section and mechanism for holding said seat in a predetermined position with respect to a horizontal plane including a tubular member extending along said main boom section having an end pivotally mounted on said carriage in a predetermined spaced relation to the pivotal axis of said main boom section ahd including a link swingably connecting the opposite end or said tubular member to said main boom section and having an eflective length substantially equal to said predetermined distance, said mechanism including a rod slidably guided in said tubular member having an end pivotally attached to said seat at a location spaced substantially said predetermined distance from its pivotal axis.

19. Hoisting apparatus comprising a shii'table carriage, a boom member shiitable between generally horizontal and generally vertical positions and comprising a main section pivotally mounted on said carriage and a relatively axially extensible section carried by said main section, a load receiving seat pivotally mounted on said extensible section and mechanism for holding said seat in a predetermined position with respect to a horizontal plane including a tubular member extending along said main boom section having an end pivotally mounted on said carriage in a predetermined spaced relation to the pivotal axis oi said main boom section and including a. link swingably connecting the opposite end oi said tubular member to said main boom section and having an eflective length substantially equal to said predetermined distance, said mechanism including a rod slidably guided in said tubular member having an end pivotally attached to said seat at a location spaced substantially said predetermined distance irom its pivotal axis, said seat positioning mechanism being adapted to hold said extensible boom section against unintended extension when said boom member is out of its generally vertical position.

20. Hoisting apparatus including a base structure, a boom member shii'tably supported on said base structure for movement from a generally horizontal to a generally vertical position, mechanism for shifting said boom member from said horizontal to said vertical position, said boom member comprising a tubular main section and an extensible section axially slidably mounted in said main section and projecting from it, mechanism for shifting said boom member from said horizontal to said vertical position, a seat pivotally mounted on the outer end or said extensible section, means for shifting said seat relative to said extensible section 0! said boom member during shifting of the latter between said positions including a guide member having a tubular part extending substantially parallel to said boom member and a substantially equal length link member connecting the end portion of said guide member to said main boom section, said guide member also including an extensible part slidably mounted in said tubular part 0! said guide member and pivotally attached to said seat. the pivotal axis 01' said seat and the pivotal connection between said seat and said extensible part of said guide member being so positioned relative to each other when said boom member is displaced from its generally vertical position as to oppose unintended extension of said boom member when it is displaced from its generally vertical position, and means for extending said extensible section of said boom member when the latter is in its generally vertical position.

21. Hoisting apparatus comprising a base structure. a boom member having a load receiving seat on one end, a carriage pivotally supporting the other end oi said boom member and shiftably mounted on said base structure, link means pivotally connected with an intermediate portion 01 said boom member and pivotaily connected with said base structure, and mechanism for shifiing said boom member from a generally horizontal to a generally vertical position comprising a shittable cylinder member carried by said carriage and a piston member fixed with respect to said base structure and slidably engaged in said cylinder and comprising means for supplying fluid pressure to said cylinder for shifting said carriage. 22. In hoisting apparatus comprising a boom member having relatively extensible piston and cylinder sections and shiitably mounted for movement between generally horizontal and generally vertical positions and comprising a piston and cylinder actuating unit for shifting said boom member from its generally horizontal to its generally vertical position; a fluid pressure supply system comprising an automatic valve having a valve housing provided with a fluid pressure inlet and first and second fluid pressure outlets. said first outlet being connected to said actuating unit and said second outlet being connected to said cylinder section of said boom member, a first valve element chamber in said housing, a first valve element shiitably mounted in said first chamber for selectively controlling the flow of fluid pressure to said first and second outlets, means yieldably holding said first valve element in position to accommodate the flow of fluid pressure to said actuating unit, a second valve chamber in said housing communicating with said fluid pressure inlet port and having large and small ports communicating with said first valve element chamber, a second shiftable valve element. in said second valve element chamber, means yieldably holding said second valve element in position to accommodate the flow or fluid pressure through said large port to said first valve element chamber and first outlet and to obstruct the flow oi fluid pressure to said small aevepos port, and means engageable by an element oi said hoisting apparatus when said boom member reaches its vertical position for shitting said second valve element to accommodate flow oi fluid pressurethroughsaidsmallportandintosaid flrstvalveelementchamber orshiitingsaidsecond valve element to a in which it obstruots reverse flow oi fluid prsmure from said flrst outlet and from said actuating unit and in which it tes flow oi fluid pressure through said second outlet for extending said boom section.

23. In hoisting apparatus comprising a boom member having relatively extensible piston and cylinder sections and shiitably mounted for movement between generally horizontal and generally vertical positions and comprising a piston and cylinder actuating unit for shifting said boom member from its horlsontal to its generally vertical position; a fluid pressure i l! system comprising an automaflc valve having a valve housing provided with a fluid pressure inlet and flrst and second fluid pressure outlets, said flrst outlet being connected to said actuating unit and said second outlet being connected to said cylinder section of said boom member. valve elements shiitably mounted in said housing for controlling the supply of fluid pressure medium from said inlet to said outlets and adapted to obstruct the reverse flow oi fluid medium from said outlets, and valve actuating mechanism including members on one of said valve elements and boom member respectively engageable only when said hoisting apparatus is in its vertical position for shirting the latter valve element to efl'ect the supply of fluid medium to said second outlet and cylinder section only when said boom member is in its vertical position.

24. In hoisting apparatus comprising a boom member having relatively extensible piston and cylinder sections and shii'tably mounted for movement between generally horizontal and generally vertical positions and comprising a piston and cylinder actuating unit and means connecting it with said boom member for shifting said boom member from its generally horizontal to its generally vertical podtlon; a fluid pressure supply system comprising an automatic valve having a valve housing provided with a fluid pressure inlet and flrst and second fluid pressure outlets. said flrst outlet being connected to said actuating unit and said second outlet being connected to said cylinder section of said boom member, valve elements shiitably mounted in said housing for controlling the supply of fluid pressure medium from said inlet to said outlets and adapted to obstruct the reverse flow oi fluid medium from said outlets, and valve actuating mechanism includin members on one of said valve elements and hoisting apparatus respectively in engagement when said boom member is in vertical position for conditioning said automatic valve to obstruct reverse flow oi' fluid pressure medium from said actuatlngimitwhilesaidboommemberisin extended condition.

25. In hoisting apparatus comprising a boom member having relatively extensible piston and cylinder sections and ahii'tably mounted for movement between generally horizontal and generally vertical positions and comprising a piston and cylinder actuating unit for shifting said boom member from its generally horizontal to its generally vertical position: a fluid pressure supply system comprising an automatic valve 75 having a valve housing provided with a fluid pressure inlet and flrst and second fluid pressure outlets, said flrst outlet being connected to said actuating unit and said second outlet being connected to said cylinder section oi said boom member, and valve shiitably mounted in said housing including valve schistingmeansresponsivetomovementolsaidboom member to and away from its vertical position ior respectively automatically admitting fluid pressure to said second outlet and cylinder section and ting the reverse flow oi' fluid pressm-e medium thereirom.

26. In hoisting apparatus comprising a boom member having relatively extensible piston and cylinder sections and shil'tably mounted for movement between generally horizontal and generally vertical positions and comprising a piston and cylinder actuating unit for shifting said boom member from its generally horizontal to its generally vertical position; a fluid pressure supply system comprising an automatic valve having a valve housing provided with a fluid pressure inlet and flrst and second fluid pressure outlets, said flrst outlet being connected to said actuating unit and said second outlet being connected to said cylinder section of said boom member, and valve mechanism shiitably mounted in said housing including valve actuating means responsive to movement or said boom member to and away from its vertical position for respectively automatically admitting fluid pressure to said second outlet and cylinder section and mecommodating the reverse flow oi fluid pressure medium therefrom. said valve mechanism being so constructed and arranged as to cause contraction of said sections of said boom member at a faster rate than the rate of shifting of said boom member from its vertical position toward its horisontal position in the event of leakage oi said fluid pressure medium from said cylinder section or from its supply from said second outlet.

27. In hoisting apparatus comprising a boom member having relatively extensible piston and cylinder sections and shiitably moimtsd for movement between generally horizontal and generally vertical positions and a piston and cylinder actuating unit for shifting said boom member from its generally horizontal to its generally vertical position: a fluid pressure supply system comprising an automaflo valve having a valve housing provided with a fluid pressure inlet and flrst and second fluid pressure outlets. saidflrstoutletbeingconnectedtosaidactuating \mit and said second outlet being connected to said cylinder section or said boom member. and valve shiftably mounted in said housing including valve actuating means responsive to movement of said boom member to and away from its vertical pomtion tor remectively automatically admitting fluid pressure to said second outlet and cylinder section and accommodating the reverse flow oi fluid pressure medium therefrom, said valve being soconstruetedandarrangedastoassureoontraction of said boom member before shitting thereoi from its vertical position in the event of leakage oi fluid pressure medium between said automatic valve and the source of fluid pressure supply thereto.

28. Hoisting apparatus including a support, aboommembermountedonsaidsupportior shitting movement between generally horizontal and generally vertical positions. means pivotally connecting the lower end of said boom member 21 with said support. a lever pivotslly connected at its lower end with said support. the lower ends of said boom member and lover beinz relatively shiitable for accommodaflnz raising and lowerinzoisaidboommembenmeansspaeedtroman intermediate portion of said boom member in the direction of its upward movement for pivotally connecting the upper end of said lever with said boom member about an axis spaced in all positions 0! said boom member a substantial distance from the plane of the pivotal axes of the lower ends oi said boom member and lever ior providina a favorable mechanical advantaze durin initial shlitina movement of said boom membe: from its generally horimntal position. and meansiorrelativelyshiitinl saidlowerendsoi 22 said boom member and lever to raise said boom member.

DAVID A. WALLACE.

REFERENCES CITED The following references are of record in the tile 0! this patent:

UNITED STATES PATENTS Number Name Date 2,085,720 Nilson June 29, 1937 2,402,572 Page June 25. 1946 2,433,900 Grime Jan. 6, i948 FOREIGN PATENTB Number Country Date 204,328 Switzerland Aug. 1, 1030 Certificate of Correction Patent No. 2,576,908 November 27, 1951 DAVID A. WALLACE It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 19, line 33, strike out boom member and insert instead hoisting apparatus; lines 34 and 35, strike out hoisting apparatus and insert instead boom member;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 4th day of March, A. D. 1952.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

